What about creating an ACTUAL Dark Knight?

[Nephyleem]

They wanted DRK to be a tank, so HP sacrificing moves were out the window. They do have a few lifestealy things like abyssal drain, soul eater, and they used to have sole survivor too.

I don't see why it have to be thrown out of the window, if the benefit you get from the sacrifice is worthy enough. (Example, paying 10% HP to get a 15~20% HP shield)
Also, what they had, and more specially what they have NOW, is FAR from what we could call useful life-stealing. It's a joke. Even the Gunbreaker's Brutal Shell is better at it.